1. Field of the Invention
The field of the invention relates to detection systems generally, and more particularly, to a portable substance identification system and method of using the same that are configured to analyze and identify at least one detection target tagged to at least one magnetic particle, which are magnetically clustered within a liquid medium on a wall of a chamber.
2. Discussion of Related Art
Personnel working in law enforcement, customs and border operations, forensics labs, military facilities, and in emergency first responder roles often need to analyze samples of unknown substances (such as pills, powders, pastes, liquids, and so forth) in the field to determine whether they comprise pathogens, explosives, pharmaceuticals, and so forth. Portable substance identification systems have been developed that deliver fast, accurate, low-cost identification of such unknown substances in the field. Such systems can objectively and non-destructively analyze and identify a broad range of detection targets in seconds. To prevent contamination and/or loss of evidence, some portable substance identification systems have the ability to analyze small quantities of detection targets (solids) that are either within their original packaging or that are placed within small containers, such as cylindrical vials formed of clear glass or plastic.
One subset of substance identification systems, employ Raman-based spectroscopic techniques to identify detection targets (defined below). Spectroscopy is a branch of physics that studies the molecular or atomic structure of a detection target by measuring and interpreting the interaction between different wavelengths of electromagnetic radiation absorbed or emitted by the detection target when it is impinged by electromagnetic radiation. In particular, Raman spectroscopy analyzes the frequency shifts from monochromatic light, usually from a laser in the visible, near-infrared, or ultraviolet range, that inelastically scatters off molecules of the detection target. Because it is very specific for the chemical bonds in molecules, the frequency shift information obtained from Raman spectroscopy provides a fingerprint by which the molecules can be uniquely identified.
The main challenge of Raman spectroscopy is separating the weak inelastically scattered laser light from the more intense elastically scattered laser light. Accordingly, several types of Raman spectroscopy have been developed. One variation, called Surface-Enhanced Raman Spectroscopy (“SERS”), involves chemisorption or physisorption of molecules of a detection target to a substrate made of or containing a metal such as silver or gold. The incident and scattered light is greatly amplified due to interactions of the light with the detection target and the metal surface.
SERS may also be used to analyze molecules of a detection target that are attached to the surface of a single metallic particle, such as a nanoparticle. A SERS-active particle contains a Raman enhancing metal and has a surface to which a Raman-active molecule(s) is(are) associated or bound. Such SERS-active particles can be used as optically responsive tags in immunoassays when bound to a receptor (antibody) that uniquely attracts a target molecule of interest. Some SERS particles (and/or SERS-active particles) are permanently magnetized, are paramagnetic or are super-paramagnetic. Materials that are either paramagnetic or super-paramagnetic become magnetized only when subjected to a magnetic field. For simplicity, the term “magnetic” will be employed hereinafter and understood to include permanently magnetized, magnetically permeable, paramagnetic, and super-paramagnetic materials and/or particles. Similarly, the term “particles” will be employed and understood to include both non-nanosized particles and nanoparticles.
The magnetizable (SERS or SERS-active) particles discussed above have been used to magnetically mix and isolate at least one detection target from a non-magnetic liquid test medium. The magnetic mixing process typically involves adding paramagnetic or super-paramagnetic particles to a liquid medium and agitating the liquid medium to bind the detection targets(s) to the particles by affinity reaction. Agitating the liquid medium is accomplished by shaking, swirling, rocking, rotating, or similarly manipulating the partially-filled container holding the liquid medium. Additionally, agitation has been accomplished by creating a magnetic field gradient in the liquid medium to induce the magnetically responsive particles to move towards the inside wall of the container, and then achieving relative movement between the magnetic source and the aggregating magnetically responsive particles to mix the magnetically responsive particles with the liquid medium and to ensure optimum binding of the detection target(s) by affinity reaction.
The isolation process has been performed by positioning a fixed magnetic source near an exterior portion of the container to immobilize the paramagnetic particles as a relatively compact aggregate on the inside wall of the container nearest to the magnetic source. A laser beam, from a laser source positioned on a side of the container opposite the magnet, is then shined through the container and onto the aggregate of paramagnetic particles, and the light scattered from the aggregate of paramagnetic particles is spectroscopically analyzed, using known techniques, to identify one or more detection targets.
The laser beam can be shined through the liquid medium, or the liquid medium can be evacuated from the container before the laser is activated. Shining the laser beam through the liquid medium, however, has several disadvantages. First, background signal(s) may be emitted from the liquid medium and/or from interfering species contained in the liquid medium. If so, the intensity of light scattered from the aggregate of paramagnetic particles must be greater than the intensity of the background signal(s) to be considered a positive indicator of the detection target(s). If the liquid medium is turbid, the laser beam may be attenuated before reaching the aggregate of paramagnetic particles or the intensity of the laser light scattered from the aggregate of paramagnetic particles may be attenuated on its way back to the detector.
A disadvantage of the known apparatus and methods that are configured to perform magnetic mixing/separation is that they are not optimized for use in portable substance detection systems that employ laser-based Raman spectroscopy. Another disadvantage is that these known apparatus and methods are not configured to form a pellet of magnetic particles such that the pellet is configured to maximize a ratio of the pellet's surface area to the pellet's volume. Yet another disadvantage is that the known apparatus and methods also are not configured to form multiple pellets that can each be interrogated by a laser beam to increase accuracy of identification.
For at least these reasons, there is a need for a portable substance identification system that is uniquely configured to: immerse at least one detection target in a liquid medium; combine the immersed detection targets and the liquid medium with magnetic, optically responsive, and/or perishable reagents; mix the detection targets, liquid medium, and the one or more magnetic, optically responsive, and/or perishable reagents; aggregate a pellet that has a maximized ratio of surface area to volume; and analyze the tagged detection target(s), if any, using laser-based Raman spectroscopy.